The Complete Aristotle (eng.)

said, with motion.
    We may start by distinguishing (1) what exists in a state of
fulfilment only, (2) what exists as potential, (3) what exists as
potential and also in fulfilment-one being a ‘this’, another ‘so
much’, a third ‘such’, and similarly in each of the other modes of
the predication of being.
    Further, the word ‘relative’ is used with reference to (1)
excess and defect, (2) agent and patient and generally what can
move and what can be moved. For ‘what can cause movement’ is
relative to ‘what can be moved’, and vice versa.
    Again, there is no such thing as motion over and above the
things. It is always with respect to substance or to quantity or to
quality or to place that what changes changes. But it is
impossible, as we assert, to find anything common to these which is
neither ‘this’ nor quantum nor quale nor any of the other
predicates. Hence neither will motion and change have reference to
something over and above the things mentioned, for there is nothing
over and above them.
    Now each of these belongs to all its subjects in either of two
ways: namely (1) substance-the one is positive form, the other
privation; (2) in quality, white and black; (3) in quantity,
complete and incomplete; (4) in respect of locomotion, upwards and
downwards or light and heavy. Hence there are as many types of
motion or change as there are meanings of the word ‘is’.
    We have now before us the distinctions in the various classes of
being between what is full real and what is potential.
    Def. The fulfilment of what exists potentially, in so far as it
exists potentially, is motion-namely, of what is alterable qua
alterable, alteration: of what can be increased and its opposite
what can be decreased (there is no common name), increase and
decrease: of what can come to be and can pass away, coming to he
and passing away: of what can be carried along, locomotion.
    Examples will elucidate this definition of motion. When the
buildable, in so far as it is just that, is fully real, it is being
built, and this is building. Similarly, learning, doctoring,
rolling, leaping, ripening, ageing.
    The same thing, if it is of a certain kind, can be both
potential and fully real, not indeed at the same time or not in the
same respect, but e.g. potentially hot and actually cold. Hence at
once such things will act and be acted on by one another in many
ways: each of them will be capable at the same time of causing
alteration and of being altered. Hence, too, what effects motion as
a physical agent can be moved: when a thing of this kind causes
motion, it is itself also moved. This, indeed, has led some people
to suppose that every mover is moved. But this question depends on
another set of arguments, and the truth will be made clear later.
is possible for a thing to cause motion, though it is itself
incapable of being moved.
    It is the fulfilment of what is potential when it is already
fully real and operates not as itself but as movable, that is
motion. What I mean by ‘as’ is this: Bronze is potentially a
statue. But it is not the fulfilment of bronze as bronze which is
motion. For ‘to be bronze’ and ‘to be a certain potentiality’ are
not the same.
    If they were identical without qualification, i.e. in
definition, the fulfilment of bronze as bronze would have been
motion. But they are not the same, as has been said. (This is
obvious in contraries. ‘To be capable of health’ and ‘to be capable
of illness’ are not the same, for if they were there would be no
difference between being ill and being well. Yet the subject both
of health and of sickness-whether it is humour or blood-is one and
the same.)
    We can distinguish, then, between the two-just as, to give
another example, ‘colour’ and visible’ are different-and clearly it
is the fulfilment of what is potential as potential that is motion.
So this, precisely, is motion.
    Further it is evident that motion is an attribute of a thing
just when it is fully real in this way, and neither before nor
after. For each thing of this kind is capable of being at one time
actual, at another not. Take for instance the buildable as
buildable. The actuality of the buildable as buildable is the
process of building. For the actuality of the buildable must be
either this or the house. But when there is a house, the buildable
is no longer buildable. On the other hand, it is the buildable
which is being built. The process then of being built must be the
kind of